ChoosePixelFormat crash

I have a PC running 64-bit Vista, with an ATI Radeon HD 4670. I updated the graphic driver to the latest available from AMD, which is from early 2011. Now, if I run a test app under Microsoft's Application Verifier, set to check Heaps, I get an access violation on ChoosePixelFormat. The Visual C++ debugger shows atigktxx.dll on top of the call stack. At this point my app hasn't done anything but register window classes and create the window for which I want to choose a pixel format. Anyone know what this is likely to mean? Does Application Verifier produce false positives, or does the driver have bad memory management, or what?